The present invention relates to surveillance systems and apparatus used to prevent shoplifting and similar unauthorized removal of articles from a controlled area. More particularly, it relates to apparatus for deactivating a surveillance tag for authorized removal from the area.
In U.S. Pat. No. 4,063,229, issued on Dec. 13, 1977, to John Welsh and Richard N. Vaughan for "Article Surveillance", and assigned to the same assignee as the present application, there is described a system wherein sensor-emitter labels or tags containing a semiconductor diode or the like are applied to articles for the purpose of surveillance. For deactivating such tags, said patent describes various devices including, among others, radio frequency generators for burning out the diode. However, such generators are disclosed as being of quite high power and are coupled inductively to the tags by way of an r.f. field. The use of such radiated fields give rise to various problems including the unknown risks to the human operators.
Said patent also describes the construction of special tags containing layers of ferrite material that can be magnetized or demagnetized by a suitable magnetic field for altering the operating characteristic of the tag and thereby deactivating the same. But the latter method complicates the tag construction and increases the cost significantly of the one component that is desired to be expendable.
Thus, it is an object of the present invention to overcome said disadvantages that are inherent in the previously known surveillance systems while hardly increasing the cost, if at all, of the expendable tags utilized. It is a further object to provide a completely safe deactivating system employing very low voltages and miniscule power, yet capable of deactivating a tag whose active element is a semiconductor diode.